This invention relates to electrodes for electrode boilers, and in particular, to such electrodes having an active material that can undergo reversible oxidation and reduction deposited on the electrode surface in contact with electrolyte to be heated.
Boiler electrodes commonly used in the prior art are made of sheet metals, such as mild steel or stainless steel, with a smooth surface typical for sheet metals after rolling or annealing. During operation with an alternating current flow, irreversible reactions occur between the electrolyte and the electrodes due to the varying electrode potential, which causes corrosion of the electrodes and contamination of the electrolyte. The corrosion and erosion of the electrodes is further enhanced by gas and steam bubble formation on the electrode surfaces. Corrosion shortens electrode life and causes accummulation of corrosion products in the circulating electrolyte solution. Furthermore, corrosion causes the formation of protrusions on the electrode surface. These conditions enhance the risk of arcing at the electrode surfaces, which further damages the electrodes.
Among the problems encountered by the prior art using sheet metal electrodes in an alternating current boiler are metal disolution and corrosion, hydrogen and oxygen evalution at higher current densities and partial discharge or arcing. Also, the prior art electrodes using steel sheets experience voltage excursions at the electrode surface which could approach two volts, thereby encountering the hydrogen evolution potential during each negative half-wave and the oxygen evolution potential during each positive half-wave of the voltage cycle. In the above-described efforts to use sheet metal electrodes, power reduction is required to limit the effects of these problems.
Accordingly, it is an object of the instant invention to provide a boiler electrode structure which avoids hydrogen evolution and oxygen evolution and allows high current density use without promoting corrosion and erosion of the electrode.
An additional object of the instant invention is to provide a method for producing an electrode having high current density capacity and low oxygen and hydrogen evolution characteristics.